The disclosed relates generally to optical switching circuits, and more particularly to optical switching circuits that employ heater resistors to control the states of optical switching elements.
Optical fibers are replacing conductive wires in telephone and data communications, since optical fibers provide extremely high bandwidth, are immune to radio frequency noise, and generate virtually no electromagnetic interference. As the cost of optical fibers decreases, use of optical fibers is expanding to applications that require switching to dynamically reconfigure the interconnection of optical signal paths.
A known approach to optical switching involves thermally controlling the presence or absence of liquid in a gap at which a plurality of optical waveguide segments intersect. This approach can be implemented for example in an optical switching circuit that includes a waveguide substrate having a plurality of thermally actuated fluidic optical switches, and a heater substrate disposed adjacent the waveguide substrate. The heater substrate includes an array of heater resistors that selectively thermally actuate the optical switches, for example by forming drive bubbles to move fluid to move into and out of gaps in the waveguide substrate that transmit or reflect light as a function of the presence or absence of fluid.
A consideration with the foregoing fluidic optical switching circuit is the non-uniform thermal characteristics of heater resistors in the heater substrate. For example, resistors closer to the middle of the heater substrate have less heat capacity than resistors closer to the edges of the heater substrate. The non-uniform thermal characteristics may degrade performance, and may also lead to reliability issues for the resistors located near the center of the heater substrate.
There is accordingly a need for an optical switching circuit heater resistor array having localized heat dissipation characteristics that are individually adjustable.
The disclosed invention is directed to a heater resistor array that includes a thin film integrated circuit sub-structure, a plurality of heater resistors defined in the thin film sub-structure, and a plurality of thermally conductive regions defined in the thin film sub-structure and dielectrically separated from said heater resistors, each of the thermally conductive regions being located proximately to an associated one of the heater resistors for dissipating heat from the associated heater resistor, wherein each of the thermally conductive regions has an area that is selected to adjust or tailor the heat dissipation capacity of the associated heater resistor. In a particular embodiment of the invention, the heater resistors are planar heater resistors while the thermally conductive regions are planar metal regions.